The invention relates to controlling the electrical power generated by engine-driven generators and the like, such as in stand-alone engine-generator sets.
Modern electrical generators, such as for supplying electrical power on board vehicles or boats, or for supplying standby power in the event of a grid power failure, employ various types of power controllers to regulate and condition the output power of the generator. Early generators were generally of the synchronous type, designed to be run at a constant speed to provide a desired frequency output. More recently, generator systems have been developed which can be run over a limited range of speeds and still provide a constant frequency output.
Frequently, generators are mounted in mobile vehicles or boats to provide on board electrical power. In marine applications, and in many land vehicle applications, such generators are coupled to a dedicated engine for rotating the generator to provide electrical power. These engine-generator sets may be speed-modulated to run at a constant speed and therefore employ synchronous power control technology, or may be speed-modulated to vary the engine speed as a function of generator load to optimize engine efficiencies, which can enable a reduction in component size and weight. Variable speed generators may also be desirable for noise-sensitive applications in which the generator will be operated frequently at low power levels. Fuel-powered engine-generator sets provide a reliable supply of AC electrical power at a desired voltage and frequency, which may be particularly useful when travelling between global regions having different AC power standards (e.g., 120 VAC at 60 Hertz in the United States and 230 VAC at 50 Hertz in many parts of Europe). Although shore power may be provided at dock berths and camp sites, for instance, such power may not be at a voltage or frequency compatible with on board electrical appliances and systems.
Self-contained engine-generator sets are sometimes provided as a complete package with mountable frame. Such self-contained systems may be supplied with a battery, such as a 12 volt DC automotive or marine battery, for providing power to start the engine. Some of the engines of these sets have separate charging systems for maintaining battery voltage.
Engine-generator sets for marine applications are frequently designed to be cooled by circulating sea water through either the engine or a liquid-to-liquid heat exchanger. By xe2x80x9csea waterxe2x80x9d, we mean water from the body of water in which the boat is afloat, which may be fresh or salt water, ocean or lake water.
According to one aspect of the invention, a power controller for controlling an engine-driven generator includes a conductor defining a DC bus for conducting electrical DC power at a DC bus voltage of at least 120 volts. The controller also includes, in electrical communication with the DC bus: a bi-directional DC-DC converter in electrical communication with a battery and constructed to transfer electrical power from the DC bus to the battery to charge the battery, and from the battery to the DC bus; a rectifier in electrical communication with the generator and constructed to rectify electrical power from the generator and to supply the rectified power to the DC bus; and an inverter constructed to convert DC bus electrical power to AC electrical power and to supply the AC power to an output connector.
In some embodiments, the power controller is constructed to supply electrical power to windings of the generator, from the battery via the DC-DC converter and the DC bus, of a polarity selected to generate torque for starting the engine.
In some preferred cases, the DC-DC converter is further adapted to transfer electrical power from the battery to the DC bus to supplement DC bus voltage during high loads.
Some embodiments also include an AC-DC converter in electrical communication with both the DC bus and an input connector, the AC-DC converter constructed to convert AC electrical power, supplied via the input connector, to DC bus electrical power. Preferably, the AC-DC converter is adapted to accept AC electrical power of one frequency, the inverter being constructed to supply AC electrical power of another frequency. The power controller may also be constructed to supply electrical power to windings of the generator, from the input connector via the AC-DC converter and the DC bus, of a polarity selected to generate torque for starting the engine.
Preferably, the power controller is adapted to maintain the DC bus voltage above at least 120 volts from a minimum generator speed to a maximum generator speed of at least 3 times the minimum generator speed.
For many applications, it is preferable that the power controller be adapted to supply at least about 2 kilowatts (in some cases, at least 5 kilowatts) of electrical power via the output connector.
In some cases, the bi-directional DC-DC converter, the rectifier, and the inverter are enclosed within a common controller housing.
Preferably, the power controller is adapted to supply at least about 1 kilowatt (more preferably, at least about 2 or even more than about 5 kilowatts, in some cases) of AC electrical power, from the battery via the DC-DC converter, the DC bus, the inverter and the output connector, with the generator off.
For some applications, the output connector has first, second and third conductors, the first and second conductors having a difference in electrical potential of about 240 volts AC, and the first and third conductors having a difference in electrical potential of about 120 volts AC.
Some embodiments include a DC bus voltage sensor connected to the DC bus and adapted to control engine speed as a function of DC bus voltage.
The power controller, in some instances, also includes a DC bus voltage sensor responsive to DC bus voltage. The controller is adapted to automatically start the engine-driven generator in response to a signal from the DC bus voltage sensor indicating a drop in DC bus voltage to a value below a predetermined minimum voltage.
According to another aspect of the invention, a power supply, for supplying electrical power on board a vehicle, is provided. The power supply includes an engine, a generator mechanically coupled to the engine for rotation to generate electrical power, and the above-described power controller electrically coupled to the generator for controlling the power generated by the generator.
According to another aspect of the invention, a marine power supply for supplying electrical power on board a boat, includes an engine adapted to be cooled by seawater, a generator mechanically coupled to the engine for rotation to generate electrical power, and the above-described power controller electrically coupled to the generator for controlling the power generated by the generator.
In some embodiments, the power controller includes an AC-DC converter in electrical communication with both the DC bus and a shore power connector, the AC-DC converter constructed to convert AC electrical power, supplied via the shore power connector, to DC bus electrical power.
Preferably, the power controller includes a controller housing, with the bi-directional DC-DC converter, the rectifier, and the inverter all enclosed within the controller housing.
The invention can advantageously perform several power transfer, manipulation and conditioning functions, the various components of the controller operating cooperatively through the high voltage DC bus in various combinations to provide useful AC power of a desired frequency and voltagexe2x80x94either from the generator or, if the generator is turned off, from a storage battery or shore power connection. In various configurations, the controller can also provide for unattended starting and stopping of the engine when necessary to charge batteries or maintain a necessary voltage. As a combination of inter-connected power manipulation xe2x80x9cmodulesxe2x80x9d, the controller of the invention offers an advantageous level of flexibility and synergyxe2x80x94particularly for providing controlled power on a mobile vehicle, such as an emergency or recreational vehicle or boat. Other advantages and aspects of the invention will be understood from the following description of embodiments, and from the claims.